1. Field of the Invention
The present invention relates to a high power LED package and a fabrication method thereof, more particularly, in which a molded part that integrally fixes frames together with a heat connecting part, and a light source is disposed above the upper surface of the molded part to optimally utilize unique beam angle thereof, thereby maximizing light efficiency.
2. Description of the Related Art
In general, an LED (Light Emitting Diode) is a semiconductor device generating light when current flows through it, and is provided in the form of a PN junction diode made of for example GaAs or GaN optical semiconductor that converts electric energy into light energy.
The light spectrum of such an LED ranges from red (e.g., 630 nm to 700 nm) to blue-violet (e.g., 400 nm) including blue, green and white lights. With such merits as low power consumption, high efficiency, and longer operation and lifetime compared with the conventional light sources such as incandescent lamps and fluorescent lamps, the demand for the LED is steadily increasing.
Recently, the LED has been expanding in its application from small-sized illumination of mobile terminals to areas such as indoor/outdoor illumination, automobile illumination, and backlights for large-sized Liquid Crystal Displays (LCD).
In the meantime, power applied to the semiconductor is increased in proportion to the intensity of light to be generated in response to current applied. Thus, with high level of power consumption, the LED typically adopts a heat connecting structure to prevent the semiconductor device and the package itself from being damaged from the heat generated during the emission of light.
FIG. 6a is a perspective view of a conventional high power LED package mounted on a board, taken vertically along an optical axis thereof, and FIG. 6b is a front elevation view of the conventional LED package of FIG. 6a. As shown in FIGS. 6a and 6b, the conventional high-power LED package 10 includes a semiconductor device 11 serving as a light source and a heat connecting structure 12 with the semiconductor device 11 mounted on the center of the upper surface thereof.
The semiconductor device 11 is electrically connected via a plurality of metal wires 13 to a plurality of lead frames 14 and thus to an external power source so as to be supplied with power.
The heat connecting structure 12 is mounted on a board 19 via an adhesion means 12a made of material of high heat conductivity in order to discharge heat, which is generated when the semiconductor device 11 emits light, thereby cooling down the package.
In the conventional LED package, the lead frame 14 is integrated to a molded part 15. The molded part 15 has an assembly hole formed therethrough so that the heat connecting structure 12 is inserted into the center of the molded part 15 to be assembled together. The lead frame 14 has one end exposed to the inside of the molded part 15 to be wire-bonded with the wire 13, and has the other end electrically connected via a pad 14a to a circuit pattern 19a printed on the board 19.
A lens 16 is provided on the upper surface of the mold part 15 to extensively spread the light generated from the semiconductor device 11 to the outside. The space between the molded part 15 and the lens 16 is filled with encapsulating material 17 made of transparent silicone resin to project the emitted light while protecting the semiconductor device 11 and the wires 1.
However, the conventional LED package 10 having such a structure entails a process of forming an assembly hole 15a and inserting the heat connecting structure 12 into the center of the molded part 15 through the assembly hole 15a. Therefore, the assembly structure and process is too complicated to be fully automated, lowering productivity. In addition, the package disadvantageously has a large volume.
A cup-shaped reflector 18 is provided in the top portion of the heat connecting structure 12 where the semiconductor device 11 is mounted. The reflector 18 is depressed downward and reflective material is applied to the outer surface of the reflector 18, by which light when emitted can be concentrated along the optical axis.
When the semiconductor device 11 generates light, the light in part is first reflected by the reflector 18, and thus concentrated forward along the optical axis. However, since the light passes the lens 16 in part directly and in part upon reflecting from the reflector 18, it should be considered in designing of the lens 16. This as a result degrades the degree of freedom in lens design.
With this arrangement of the semiconductor device 11, the top portion of the molded part 15 or of the heat connecting structure 12 partially blocks the light generated to restrict or narrow view angle or beam angle that is a diverging angle of the light. Thus, this LED package type is not suitable for an illumination light source that is required to uniformly light a wide area by optimally using the unique beam angle of the semiconductor device 11.
Furthermore, in assembling of the lens 16 with the encapsulating material 17 interposed between the molded part 15 and the lens 16, the encapsulating material 17 may flow out of the lens 16, soiling the lead frames 14 and adjacent components.
In the meantime, U.S. patent publication No. 2004/0075100 (published on Apr. 22, 2004) discloses an LED package structure including a heat connecting part with a semiconductor device mounted thereon as a light source, a lead frame connected to the heat connecting part and a molded part injection-molded to integrally fix the heat connecting structure with the lead frame. In corresponding regions of the molded part and the heat connecting part where a semiconductor device is mounted, there is formed a cup-shaped reflector depressed downward to reflect light.
This LED package structure may omit an assembling process of the heat connecting part by providing a molded part to wrap both of the heat connecting part and the lead frame through injection molding. However, an additional process is needed in which the heat connecting part is connected with the lead frame before the injection molding. Furthermore, this structure also has a defect in that an electrode of the lead frame is susceptible to short-circuit under external impact.
Moreover, with the arrangement of the semiconductor device, the top portion of the molded part partially blocks the light generated to restrict or narrow the beam angle of the light. Thus, this LED package structure is not suitable for an illumination light source that is required to uniformly light a wide area by optimally using the unique beam angle of the semiconductor device.
Such conventional LED packages have an up-set lead frame structure, in which the lead frame is bent at a lower end in parallel to the board, bent upward at a right angle or sloped upward, and bent at an upper end in parallel to the board toward the device. In this structure, the intermediate portions and the lower end of the lead frame are excessively protruded out of the molded part, and when the package is mounted on a board of an application device, occupy a large area on the board, which is an obstacle to the miniaturization of the application device.
Moreover, the lead frame is bent after the injection molding, the electrode is highly susceptible to short-circuit or defect owing to external force generated by the bending process.